This relates generally to electronic devices, and, more particularly, to wireless electronic devices that use two-way time-of-flight ranging techniques to ascertain the distance between a pair of devices.
Wireless electronic devices can communicate using a variety of wireless communications protocols. For example, cellular telephone communications protocols may be used to allow cellular telephones to communicate with wireless base stations and wireless local area network protocols such as the IEEE 802.11 protocol may be used by wireless devices to communicate with wireless routers.
Low power communications protocols such as the IEEE 802.15.4 ultra wide band standard are used in wireless sensor networks and systems that support real time location services. It may sometimes be desirable to ascertain the distance between devices. In a typical scenario, a pair of devices may exchange timestamped wireless messages and may analyze the time stamps in the messages to determine the range between the two devices. Appropriate actions may then be taken based on the range information extracted from the messages. For example, a wireless key fob may be permitted to unlock a vehicle door only if the wireless key fob is determined to be within close proximity to the vehicle. For applications such as these, it is desirable for range measurements to be made accurately to prevent unauthorized access to the vehicle.